Yes use your chest circumference measurement and this should work out fine.
Your back width is close to your shoulder width. This is normal, most people’s back armscye curve is a bit flat and shallow. The example bodice in your book is a bit exaggerated.
You may find that you need to add a dart in the shoulder seam to make your bodice’s shoulder length match your actual shoulder length.
If point G isn’t high enough for your neck and shoulder muscles then you should create a new measurement from neck side down to waist level at the back (Valentina’s neck_side_to_waist_b). some systems call this the Full Back Length. Set D’s formula to use this measurement from A, then G will be at the correct place for the side of your neck.
I’m curious, why isn’t bust circumference the same as chest circumference? Vocabulary can be confusing when discussing measurements. Maybe you’re using a book which prescribes this terminology, or there may be language translation issues at play here. Here’s the terminology that I’m familiar with, which is by no means authoritative:
Bust and chest refer to the same measurement around the fullest part of the breasts.
High bust or upper bust is the measurement right under the arm above the breasts.
Low bust or under bust or rib cage is the measurement right underneath the breasts.